Pyrotechnic propellant charge



Oct. 6, 1964 A. J. SCHERMULY 3,151,559

PYROTECHNIC' PROPELLANT CHARGE Filed June 12, 1962 2 Sheets-Sheet 2 INVENTOR.

Oct. 6, 1964 A. J. SCHERMULY 3,151,559

PYROTECHNIC PROPELLANT CHARGE Filed June 12, 1962 2 Sheets-Sheet 1 A Home y United States Patent .0

3,151,559 PYROTECHNIC PROPELLANT CHARGE Alfred James Schermuly, Newdigate, Dorking, England, assignor to The Schermuly Pistol Rocket Apparatus Limited, Newdigate, Dorking, England, a British company Filed June 12, 1962, Ser. No. 201,943 Claims priority, application Great Britain, June 20, 1961, 22,199/ 61 12 Claims. (Cl. 10298) This invention relates to an improved method of manufacturing a pyrotechnic propellant charge. The invention is also concerned with an improved pyrotechnic device comprising a propellant charge made by the method of the invention.

Conventional pyrotechnic propellant charges are made by compacting a suitable pyrotechnic composition within a rigid tubular casing. Normally the charge is formed with a conical recess extending into the body of the charge from the choke end thereof. When the charge is to be fired, for example when a rocket comprising the charge is launched, an initiating flash is led into the recess to ignite the exposed layer of the charge. To obtain an even burning charge and to avoid cavities in the composition it has been found necessary to compact the charge stage by stage, compacting a layer of the composition on top of previously compacted layers. The formation of large propellant charges by conventional techniques is therefore an expensive and time-consuming process.

According to one feature of the present invention an improved method of making a pyrotechnic propellant charge comprises collapsing a tubular metal container, by the application of pressure thereto, around a granular pyrotechnic propellant composition contained therein to compress the composition into a unified charge.

Preferably the tubular container is made of a soft metal and has thin walls so that the resistance of the container to collapse is small. The container may be of any convenient cross-section, for example circular, elliptical, rectangular or square, although the preferred cross-section is circular. It is preferred to apply the pressure to the container in an axial direction, so that the container is collapsed axially, but the invention is not limited to this. For example a container of rectangular cross-section may have pressure applied thereto in a direction to collapse the container to one of substantially square section. It is convenient to completely fill the container with granular composition prior to applying pressure to the container.

The actual reduction in volume between composition and compressed charge will depend on the actual charge used but will normally be between 30 and 70%.

The granular propellant composition may be any of the compositions known and used in the art. Standard black compositions (based on gunpowder) or perchlorate compositions are particularly suitable. The resultant charge produced by the employment of the method of the invention, burns very evenly and it has been found that faster burning compositions may safely be employed to make a charge in accordance with the invention, than could, with equal safety, have been used to make a charge using conventional techniques. Propellant charges produced by the method of the invention are very stable and may be handled and machined without fear of disturbing the main body of compacted composition or of breaking the bond formed during the collapsing of the container between the composition and the container wall.

The container may be compressed on a conventional hydraulic press. To prevent splitting of the container during compression it is convenient to compress the container while it is retained within a mould. Conveniently the mould is demountable so that the compressed con tainer can easily be removed from the mould. It is conrocket according to the invention having a given weight 3,151,559 Patented Oct. 6, 1964 that during the pressing operation the axial compression of the container is not accompanied by any substantial increase in the cross-sectional area of the container.

If the container filled with composition were to be subjected to compression applied wholly from one end the resultant charge would have a greater density at the end to which the compression had been applied than at the other end. To achieve a more uniform charge it is preferred to effect some of the total desired reduction in length of the container by collapse from one end of the container and then to effect the remaining reduction in length by collapse from the other end of the container.

As the container is compressed axially it forms a series of irregular internally projecting convolutions. In practice these convolutions become embedded in the compacted charge during the pressing operation so that the container and charge become firmly bonded together.

A thrust-time graph for a conventional pyrotechnic propellant charge having a conical recess therein exhibits a sharp peak close to the origin followed by a marked decrease in thrust, which decrease continues steadily until the charge is fully burnt out. The initial peak of thrust is useful for stabilising a rocket at launching but the marked decrease in thrust after the initial peak means that with conventional charges most of the driving power for a rocket comes shortly after launching and very little comes in the later stages of the combustion of the'charge.

A thrust-time graph of a charge prepared in accordance with the method of the present invention exhibits a substantially uniform thrust throughout virtually the entire ing a small auxiliary booster charge.

According to a further-feature of the invention a pyrotechnic device comprises a-propellant charge formed by collapsing a tubular metal container around a granular pyrotechnic propellant composition contained therein to compress the composition into a unified charge.

'A rocket according to'the invention, having a given thrust, can be'made smaller and more compact than a conventional rocket of the same thrust. Similarly .a

of charge can be made to have a greater range, or be capable of carrying a heavier load, than a conventional rocket having a comparable weight of charge.

Features of the invention will now be described, by way a of example with reference to the accompanying drawing,

in which: I

FIGURE 1 is a cross-sectional view of a tubular coni tainer filled with propellant composition, T

. container of FIGURE 1 after axial compression,-

FIGURE 2 is a'partially cross-sectioned view, of the FIGURE 3 is asectional view of a part of a rocket employing charges formed as illustrated in FIGURES 1 and 2, and

FIGURES 4-8 illustrate successive steps'of carrying out the method of the present invention.

Referring to FIGURE 1 a container 1 is formed from an aluminum tube 7.5 inches (19 cms.) long, with an external diameter of 1.25 inches (3.2 cms.) and 'a wall 70.

thickness of 0.008 inch (0.2 mm.). One end of the tube is rolled over as at 2 to leave a circular opening. 3 and a disc of muslin 4 is stuck across the opening 3. With the disc 4 lowermost, a black granular pyrotechnic propellant composition 5 of conventional mix is poured into the container 1 and well shaken down until the composition almost reaches to the top. A steel disc 6 is then placed on the top of the composition and the end of the container rolled around the disc 6, as at 7.

The container 1 is then placed in a three part mould which, when assembled, has a central circular cavity therethrough slightly over 1.25 inches (3.2 cms.) in diameter. The mould is then placed between aligned up-stroking and down-stroking rams of a hydraulic press, each ram terminating in a punch slidable within the cavity in the mould. Pressure is first applied by the down-stroking ram and a reduction in the length of the container of 2.5 inches (6.5 cms.) is achieved. Pressure is then applied by the up-stroking ram and a further reduction in length of 2 inches (5 cms.) is obtained. The container 1 now has a length of 3.0 inches (7.5 cms.) and appears as illustrated in FIGURE 2.

The reduction in length of the container has produced a series of internally projecting convolutions 8 and has at the same time, compacted the granular composition 5 into a unified charge 9. The compressed container can be removed from the mould by dismantling the latter. The charge is then available for use in a rocket.

Because of the special properties of a charge made in accordance with the invention it is possible to construct serviceable rockets using a lighter casing to contain the charge that has hitherto been possible. Part of a rocket is shown in FIGURE 3. Two charges are employed in this rocket, a main charge 10 and a booster charge 11. The main charge 10 and the booster charge 11 (for convenience shown without the convoluted walls) are retained within a light alloy case 12, between a circumferentially rolled projection 13 and an apertured choke plate 14. The choke plate 14 is retained within the case 12 by rolling an end of the latter as at 15. The booster charge 11 has been machined from a compacted charge as shown in FIGURE 2 and has an aperture 16 passing therethrough and a frusto-conical ignition surface 17. The ignition surface 18 of the main charge 10 is plane. The surfaces 17 and 18 define a combustion chamber 19. When the rocket is fired a flash is led, by a suitable flash tube (not shown), from a detonator (also not shown) into the combustion chamber 19 to initiate ignition of the charges 10 and 11 over the surfaces 17 and 18, respectively. The volume of gas escaping through the choke plate 14, and thus the thrust of the rocket, depends on the area of the burning charge. Initially the whole of the surface areas 17 and 18 are burning so that the initial thrust is more than twice that existing if the plane surface 18 alone were burning. The gases generated in the combustion chamber 19 stream through the aperture 16 and the choke plate 14 to drive the case 12 through the air. When the booster charge has burnt away the thrust drops to a value corresponding to combustion over the plane surface defining the cross section of the charge It) (i.e. the same surface area as surface 18) and is maintained substantially constant at this value until virtually all the charge It) has been burnt. The additional thrust developed by the booster charge 11 assists in imparting stability to the rocket during the initial stages of the flight. Clearly the initial thrust can be controlled by varying the surface areas of the charges exposed to the combustion chamber 19. Thus for example instead of leaving the charge 10 with the plane surface 18, initial thrust could be increased by providing the charge 10 with a conical surface 20 (shown dotted). In some applications where it may be desirable to pass the initiating flash through to a pyrotechnic device mounted in the head of the rocket, a recess 21 (shown dotted) may be provided in the main charge 10. To prevent the flash igniting the charge exposed around this recess 21, the exposed areas may be varnished or the recess lined with a metal tube.

The method of the present invention is illustrated in FIGURES 4-8.

As illustrated in FIG. 4, the container 41 filled with the granular material 42 is first introduced into a mold 43 the cavity of which is of substantially the same cross sectional dimensions as the container 41, in other words, into which the container 41 fits with very little free space left outside the lateral wall of the tubular container.

Thereafter, as shown in FIG. 5, pistons 51 and 52 are positioned next to the opposite end walls 53 and 53, respectively of the container in the mold, which pistons are capable to exert pressure in axial direction of the container. As shown in FIG. 6, upon downwardly pushing the upper piston 51 while holding the container by means of the lower piston 52 which is not moved at this time, the upper portion of the container is compressed and the material therein compacted. Upon then moving the lower piston 52 upwardly while keeping the upper piston 51 stationary, as shown in FIG. 7, the lower portion of the container is compressed and the material therein compacted. Finally, the thus compacted container, now indicated by reference numeral 81, with the compressed material therein is pushed out of the mold as shown in FIG. 8.

What is claimed is:

1. A method of making a pyrotechnic propellant charge, comprising the steps of introducing into a thinwalled metal container a granular pyrotechnic propellant; and subjecting said container with said granular propellant therein to pressure in two opposite directions so as to compress and reduce the length of said container in said opposite directions, while simultaneously substantially preventing expansion of said container in any direction, thereby compacting said propellant in said container and forming in the wall thereof internally projecting convolutions embedded in the compacted propellant.

2. A method of making a pyrotechnic propellant charge, comprising the steps of introducing into a thinwalled tubular metal container a granular pyrotechnic propellant; and subjecting said container with said granular propellant therein to pressure in axial direction thereof so as to compress and reduce the length of said container while simultaneously substantially preventing lateral expansion thereof, thereby compacting said propellant in said container and forming in the tubular wall thereof internally projecting convolutions embedded in the compacted propellant.

3. In a method of making a pyrotechnic propellant charge, the step of subjecting a thin-walled, granular propellant-containing metal container to pressure in opposite axial directions so as to compress and reduce the axial length of said container while simultaneously preventing lateral expansion of the same, thereby compacting said propellant in said container and forming in the tubular wall of the latter internally projecting convolutions embedded in the compacted propellant. 4

4. In a method of making a pyrotechnic propellant charge, the step of subjecting a thin-walled, granular propellant-containing closed metal container to simultaneous pressure in opposite axial directions so as to compress and reduce the axial length of said container by said simultaneous application of pressure in said opposite axial directions, while simultaneously preventing lateral expansion of the same, thereby compacting said propellant in said container and forming in the tubular wall of the latter internally projecting convolutions embedded in the compacted propellant.

5. A method of making a consolidated pyrotechnic pro pellant charge, comprising the steps of filling a right cylindrical thin-walled tubular metal container-of circular cross-section with a granular propellant; placing the filled container into a mold cavity corresponding to the crosssectional shape of said container but being longer in axial direction than the latter; applying pressure to the end faces of said container in said mold so as to compress the same without increasing the lateral dimensions of said container due to its confinement in said mold, thereby compacting said propellant in said container and forming in the tubular wall of the latter internally projecting convolutions embedded in the compacted propellant; and removing the thus compressed container with the compacted propellant therein from said mold cavity.

6. A method of making a consolidated pyrotechnic propellant charge, comprising the steps of filling a right cylindrical thin-walled tubular metal container of circular cross section with a granular propellant; placing the filled container into a mold cavity corresponding to the crosssectional shape of said container but being longer in axial direction than the latter; applying in a single stroke, respectively pressure to each of the end faces of said container in said mold so as to compress the same without increasing the lateral dimensions of said container due to its confinement in said mold, thereby compacting said propellant in said container and forming in the tubular wall of the latter internally projecting convolutions embedded in the compacted propellant; and removing the thus compressed container with the compacted propellant therein from said mold cavity.

7. A method of making a consolidated pyrotechnic propellant charge, comprising the steps of filling a right cylindrical thin-walled tubular metal container of circular cross-section with a granular propellant; placing the filled container into a mold cavity corresponding to the cross sectional shape of said container but being longer in axial direction than the latter; applying successively in a single stroke, respectively pressure to each of the end faces of said container in said mold so as to compress the same without increasing the lateral dimensions of said container due to its confinement in said mold, thereby compacting said propellant in said container and forming in the tubular wall of the latter internally projecting convolutions embedded in the compacted propellant; and removing the thus compressed container with the compacted propellant therein from said mold cavity. v

8. A method of making a consolidated pyrotechnic propellant charge, comprising the steps of filling a right cylindrical thin-walled tubular metal container of circular cross-section with a granular propellant; placing the filled container into a mold cavity corresponding to the cross sectional shape of said container but being longer in axial direction than the latter; applying simultaneously in a single stroke, respectively pressure to each of the end faces of said container in said mold so as to compress the same without increasing the lateral dimensions of said container due to its confinement in said mold, thereby compacting said propellant in said container and forming in the tubular wall of the latter internally projecting convolutions embedded in the compacted propellant; and removing the thus compressed container with the compacted propellant therein from said mold cavity.

' latter internally projecting convolutions embedded in the 1 9. A method of making a consolidated pyrotechnic propellant charge, comprising the steps of filling a right cylindrical thin-walled tubular metal container of circular cross-section with a granular propellant; placing the filled container into a mold cavity corresponding to the cross sectional shape of said container but being longer in axial direction than the latter; applying in a single stroke, respectively, pressure to each of the end faces of said cont-ainer in said mold so as to compress the same to between 30 and of its original volume without increasing the lateral dimensions of said container due to-its confinement insaid mold, thereby compacting said propellant in said container and forming in the tubular wall of the compacted propellant; and removing the thus compacted container with the compacted propellant therein from said mold cavity.

10. A method of forming in an enclosure a compacted granular mass, comprising the steps of introducing a granular mass into a thin-walled metal container; and subjecting said container with said granular mass therein to pressure in two opposite directions so as to compress and reduce the length of said container in said opposite directions, while simultaneously substantially preventing expansion of said container in any direction, thereby compacting said mass in said container and forming in the wall thereof internally projecting convolutions embedded in the compacted mass.

11. A compacted pyrotechnic propellant charge, comprising, in combination, a thin-walled metal container formed with internally projecting convolutions in a portion of the wall thereof; and a compacted pyrotechnic propellant filling said container with said internally projecting convolutions of said wall portion embedded in said compacted propellant.

12. A compacted pyrotechnic propellant charge, comprising, in combination, a closed thin-walled tubular metal container formed with internally projecting conv=olutions in the tubular wall thereof; and a compacted pyrotechnic propellant filling said container with said internally projecting convolutions of said wall portion embedded in and pressing against said compacted propellant.

References Cited in the file of this patent UNITED STATES PATENTS 349,718 -Hollerith et al. Sept. 28, 1886 882,154 Lheure Mar. 17, 1908 1,041,406 Bauroth Oct. 15, 1912 1,901,852 Stolfa et al. Mar. 14, 1933 2,114,214 Damblanc Apr. 12, 1938 2,637,274 Taylor et al. May 5, 1953 2,877,709 Duckworth Mar. 17, 1959 2,921,521 La Haye et al. Jan. 19, 1960 

11. A COMPACTED PYROTECHNIC PROPELLANT CHARGE, COMPRISING IN COMBINATION, A THIN-WALLED METAL CONTAINER FORMED WITH INTERNALLY PROJECTING CONVOLUTIONS IN A PORTION OF THE WALL THEREOF; AND A COMPACTED PYROTECHNIC 